The long-term objective of this project entitled Passive Mapping of Sensori-Motor Somatotopy at fMRI seeks to capitalize on existing cortical sensori-motor integration, using passive stimulation techniques and devices to map comprehensively the sensori-motor homunculus at fMRI. Passive movements are known to cause similar patterns of activation in the sensori-motor cortex compared to that of active movements. For comprehensive mapping of the sensori-motor homunculus in human patients, however, active and passive movement paradigms are impractical. In this Phase I proposal, we will address the feasibility of utilizing passive, motionless stimulation paradigms and devices to localize the somatotopic organization of the primary sensori-motor cortex, without inducing significant head motion. Specific Aim 1. Deep tissue stimulation: Primate studies indicate that M1 activation in response to passive motion is largely due to deep tissue (i.e. muscle) receptor afferents. Deep tissue (i.e. muscle) manual and pneumatically driven pressure stimulation will be used to activate the sensori-motor cortex in humans. The location of cortical activation will be validated against that induced by comparable voluntary movements. Specific Aim 2. Sensory receptor depolarization: Primate studies indicate that a significant proportion (25%) of sensory driven M1 cortex activation is caused by surface receptor input. Direct electrical depolarization of surface sensory receptors and/or deep tissues (i.e. muscle) will be used to drive the activation of sensorimotor cortex in humans. The location of cortical activation will be validated against that induced by comparable voluntary movements. Specific Aim 3. Optimizing the location of body part stimulation: In primates, sensory stimulation causes somatotopically coupled efferent zones of the motor cortex to activate, but this is body-site-specific (i.e. flexor or extensor side). Optimal locations in humans for passive stimulation of specific body parts to produce M1 cortex efferent zone activity will be determined. Health relatedness: Because the technology will eliminate the problem of head motion and, when combined with other post-processing developments such as temporal phase mapping and functional field mapping, will dramatically improve time-efficiency, the benefits of fMRI will be brought to a significantly greater number and variety of patients. The technology is enabling, and will have significant applications beyond fMRI and beyond imagine} to study the sensori-motor system in the human brain.